The present invention relates generally to an apparatus for filtering a high pressure fluid stream and, more particularly, to a filter assembly for removing bacteria and other foreign materials from high pressure physiologic fluid streams.
In many applications it is desirable to remove bacteria and other foreign materials from fluids prior to delivery of the fluids to a particular desired location. For example, in the medical field, fluids routinely are filtered for sterilization in conjunction with their delivery to catheters for infusion into a patient. Typically, such filtering is accomplished by the placement of a filter media comprising a porous membrane in the fluid flow path.
There are many different types of commercially available filter media, e.g., nylon, polyethersulfone, teflon, polycarbonate, polyester, polytetrafluoroethylene, polypropylene, cellulose, glass fiber, stainless steel, monel, inconel, silver and gold. A filter membrane generally may be described by its xe2x80x9cmean path,xe2x80x9d i.e., the average size of the pores in the filter media, and/or its xe2x80x9cabsolute path,xe2x80x9d i.e., the size of the largest pores in the filter media. A filter membrane""s absolute path corresponds to the size of the smallest particle that can be filtered out of a fluid flow path by the filter membrane. For medical applications in which absolute sterilization is required, a filter membrane having an absolute path of not greater than about 0.2 micron typically is required.
Filter membranes come in a variety of shapes and sizes. Filter membranes may be mounted in line or in panel, and they are typically disposed within a filter holder, either alone or in combination with additional pre-filters, screens, etc. For examples of commercially available filter devices, see, e.g., the 1995 Microfiltration and Laboratory Products Catalog, Poretics Corporation, Livermore, Calif.
Many fluids to be infused into patients are not delivered from a high pressure source, e.g., pressures up to about 5500 p.s.i. or higher. For that reason, conventional fluid filtering devices such as those referred to above typically are not designed to withstand high pressure environments. Under high pressure conditions, the porous membranes of conventional filter devices may burst, allowing bacteria and other unwanted materials to pass. Accordingly, there remains a need for a filter assembly capable of removing bacteria and other foreign materials from high pressure fluid streams.
The present invention may address one or more of the problems set fourth above.
Certain aspects commensurate in scope with the disclosed embodiments are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
The copending U.S. patent application entitled xe2x80x9cFiltration of Gas-Containing Fluidsxe2x80x9d filed on Apr. 30, 1999, by James Richard Spears, Ser. No. 09/302,978, is hereby incorporated by reference herein for all purposes.
In one embodiment of the present invention, an apparatus for filtering a high pressure fluid stream is provided. Advantageously, the high pressure fluid stream comprises a flow of a fluid in which a gas (e.g., oxygen, nitrogen, carbon dioxide, air) is dissolved. Advantageously, the dissolved gas volume normalized to standard temperature and pressure is between about 0.5 and about 3 times the volume of the solvent. The fluid passing through the filtering apparatus advantageously comprises a fluid to be provided at a given site in a gas-supersaturated state. Examples (without limitation as to the scope of the present invention) include fluids that are to be delivered into blood, infused into a patient, brought into contact with tissues, etc., such as oxygen-supersaturated fluids.
The apparatus comprises a filter assembly stack disposed within a filter housing assembly. The filter assembly stack comprises a first o-ring, a filter membrane, a membrane backing member, and a second o-ring. The filter housing comprises a bulkhead and a cap.
The filter assembly stack and the housing assembly advantageously are adapted and assembled so that when the cap and bulkhead are joined, e.g., by threaded engagement, with an adhesive, etc., the o-rings are compressed, so as to create a sealed continuous fluid flow path through the filter assembly stack and filter housing assembly. Advantageously, the first o-ring, the filter membrane, and the membrane backing member are disposed between the bulkhead and cap, with the filter membrane disposed between the first o-ring and the membrane backing member, so that a portion of the cap (e.g., a generally centrally disposed annular shoulder region) presses against part of the membrane backing member so as to compress the first o-ring to create a first seal between the bulkhead and the filter membrane. A second seal advantageously is created by compression of the second o-ring between the bulkhead and cap.
The membrane backing member advantageously comprises a filter frit having a mean path about equal in size to the absolute path of the filter membrane, e.g., advantageously about 0.2 micron. Advantageously, the filter frit comprises a sintered metal filter disk made of titanium, stainless steel, monel, inconel, gold, or another suitable filter material. The frit is disposed downstream of the filter membrane, so as to provide backing support to prevent the filter membrane from bursting under high fluid pressures. A mesh, screen, or other fluid permeable device for providing support, or any combination of one or more of such devices, also may be used instead of or in addition to a filter or a frit as a filter membrane backing member. Advantageously, the filter membrane backing member comprises a relatively smooth member free of sharp edges or rough surfaces that would compromise the filter it backs under pressure.
In an alternate embodiment, the filter assembly stack comprises a filter frame, an o-ring, one or more filter membranes, a membrane backing member, and a filter frame cap. The filter assembly stack advantageously comprises two filter membranes disposed between an o-ring and a membrane backing member. The o-ring, filter membranes, and membrane backing member advantageously are held together between the filter frame and the filter frame cap, with a portion of the filter frame cap pressing against part of the membrane backing member so as to compress the o-ring to form a seal with the filter membrane. The joint between the filter frame and filter frame cap may be sealed with an adhesive, e.g., a UV adhesive. Thus, a sealed fluid pathway through the filter assembly stack is provided. The filter assembly stack is disposed within the filter housing with one or more seals, such as o-rings, disposed between the filter assembly stack and the filter housing bulkhead and cap, to ensure a sealed fluid pathway through the entire assembly. Alternatively, the filter housing bulkhead and cap are adapted with one or more embossed surfaces (raised portions, e.g., formed by one or more ridges or by one or more grooves in the assemblies) that contact the filter frame or filter frame cap upon assembly. Advantageously, the contacting portions of the ridges and/or filter stack are made of deformable materials that compress to form a seal when the filter housing bulkhead and filter housing cap are joined, so that the filter assembly is self-sealing. Alternatively, the filter frame and/or filter frame cap may be adapted to include one or more of such ridges so that the filter assembly is self-sealing, or an o-ring or other such sealing device may be used.